Louisiana announced 17 new West Nile virus infections Friday, making this year’s outbreak the worst since the mosquito-borne virus was first detected in the state. With this report, the 2012 case count rose to 338, 10 more than the previous high of 328, which was established in 2002.

Although that total is the highest since West Nile record-keeping began in Louisiana, health-department spokesman Ken Pastorick pointed out that the 43 people this year who have been infected but showed no symptoms were in a category that did not exist in 2002. With those people removed from the count, the total falls to 295, 33 below the 2002 mark.

The state health department also reported one virus-related death on Friday, bringing this year’s toll to 13. The highest total – 24 – was recorded in 2002. The Department of Health and Hospitals does not announce the home parishes of people who succumb to West Nile complications.

Although most infected people never know they are carrying the virus because their immune systems repel it, there are two complications: West Nile fever, which produces flu-like symptoms, and neuroinvasive disease, which causes swelling in the brain and spinal cord and can be fatal.

In the latest report, there were five reported cases of neuroinvasive disease, including one in New Orleans and another in Jefferson Parish. The other three were in Bossier, Calcasieu and West Feliciana parishes.

There also were 11 new cases of West Nile fever: four in East Baton Rouge Parish, two in Caddo Parish and one each in Ascension, Beauregard, Calcasieu, DeSoto and Lafourche parishes.

One person in Lafourche Parish had been infected but displayed no symptoms. Such cases are diagnosed when the virus is found in the bloodstream of people whose blood has been drawn for any number of reasons, including a blood donation or an annual physical examination.

Nationally this year, there have been 4,725 infections and 219 deaths, making the outbreak the worst since 2003, according to the federal Centers for Disease Control and Prevention.

Louisiana is one of eight states that account for nearly 70 percent of the cases, CDC data show. The other states are California, Mississippi, Illinois, South Dakota, Michigan, Oklahoma and Texas.

Texas has recorded 1,628 infections, more than one-third of the national total, according to the CDC.

Health officials in Louisiana have suggested that a combination of factors led to this year’s high count: a relatively mild winter, an early spring and a hot summer, all of which are conducive to mosquito breeding.

People most vulnerable to West Nile complications are the very old, the very young and people with immune-system problems.

Because there is no treatment for West Nile infection except supportive care, health officials recommend preventive measures such as staying indoors around dusk and dawn, when mosquitoes are most likely to swarm; wearing long sleeves and trousers when going outside; eliminating standing water; ensuring screens are secure; avoiding perfume that might attract insects; and using insect repellent containing DEET.